This invention relates to an adjustable mounting means for controlling and permitting modification of the spacing between the stringplate and the adjacently-spaced soundboard of a musical instrument, such as a piano.
In the construction of a piano, the stringplate, to which the opposite ends of the strings struck by the hammers are fastened, is maintained in a spaced relation to an adjacently-spaced soundboard. The stringplate is subjected to enormous torsional and compressive forces since a multiplicity of strings of varying tensions are affixed to opposite ends thereof. As a result, the stringplate is typically a cast iron member of substantial thickness and weight to ensure that it does not experience significant dimensional changes or warping over a long period of time. Dimensional changes are likely to alter the tones produced during use thus producing a lower-quality sound and may only be partially compensated for by retuning the string tension.
The conventional stringplate is provided with a number of different openings which permit bridges contained on or mounted against the adjacent soundboard to extend through the plane of the stringplate and thereby contact the strings. The contact of the bridges with the strings produces a departure from a linear string position. The relationship between the location of the bridges between ends of the strings, the number of strings associated with each bridge and the spacing between the adjacent bridges has been the study of many craftsmen for a long period of time. These relationhips are fixed once the design of the piano is completed. However, different environmental conditions along with any movement of the piano may result in an undesired change in the tension of the strings. This verification can result from the changes in the stringplate itself, dimensional changes in either the soundboard which supports the bridges or the frame, or a combination of these factors. However, it is important to note that these frequently unpredictable variations adversely affect performance and that compensation techniques should be used as a result of these changes. In practice the resultant impact on the sounds produced by the individual strings cannot always be corrected by adjusting individual string tension and may require removal of the stringplate from the piano frame in certain instances.
The peripheral frame is an integral part of any piano and its design is such as to ensure that the substantial weight of the stringplate can be borne for the useful life of the piano. In addition to supporting the stringplate, the frame provides support for the soundboard which is firmly affixed thereto about its periphery. In order to establish uniform spacing between stringplate and soundboard during manufacture, it has been common to provide spacers between the stringplate and the underlying soundboard. These spacers are subjected to compressive forces over a long period of time and may themselves change dimension which further exacerbates the problems noted above.
In addition, the spacing between the strings and the underlying soundboard determines in part the tone produced by each string and this spacing should be precisely maintained over long periods of time in order to provide a reliable musical instrument. Variations in the stringplate or soundboard dimensions or their relative positions across the entire large area surfaces thereof will produce different tones and sound quality when the strings are vibrated. Thus, a means of compensation is needed to ensure that the effects of these changes can be reversed and the original or better tone quality is restored or improved.
The difficulties encountered with the use of spacers distributed about the periphery of the stringplate and resting on the underlying support frame are discussed in U.S. Pat. No. 3,437,000 which is directed to a means for mounting the stringplate in a predetermined space relation to the support frame. This patent teaches the use of bolts which are threaded into the stringplate and the adjacently spaced portions of the underlying frame for stringplate support. The stringplate is maintained initially at the desired height by the use of intermediate spacers in combination with the bolts threaded through tapped holes in the stringplate and into the underlying frame. The bolts are turned until the heads thereof rest firmly against the exposed surface of the stringplate. Thus, the height of the stringplate over the combination of sounding board and frame is determined by the spacers or supports positioned prior to the lowering of the stringplate into position in the piano. The bolts are not suited for later adjustment of the height of the stringplate as the spacing is determined by the blocks which may be left in place or removed, according to the reference. When the mounting is completed, the stringplate is out of contact with the soundboard and supported, at least initially, in the proper position about its periphery. This method of construction provides one mode of assembly for a grand piano, but it does not permit any later adjustment to compensate for variations provided by changes in location of the piano, different environmental conditions as affecting on the plurality of the stringplate or the spacing between the plate and the adjacent soundboard. In summary, this reference teaches establishing a one-time fixed relationship between frame-soundboard combination and the adjacently-spaced stringplate which cannot be readily modified without disassembling the entire piano structure.
Accordingly, it is an object of the present invention to provide a positive means for supporting a stringplate in spaced relationship to the soundboard and to do so in a manner which permits modification of the spacing at different points about the periphery of the stringplate to compensate for changing conditions. In addition, this invention is directed to a mounting means which permits localized adjustment with the adjustments being made from the underside of the piano. The adjustments provided by the present invention are bidirectional in the sense that both increasing and decreasing of the spacing between stringplate and soundboard can be readily accomplished in localized areas, as necessary. Furthermore, the physical support of the stringplate does not rely on the load bearing capability of tapped apertures in the stringplate, but rather utilizes relatively large area support regions adjacent the apertures of the stringplate and located on the undersurface thereof.